In and of itself

Looks like there's no difference:

http://www.xrefer.com/entry/633061

There's a functional difference. "In itself" is a more ambiguous construction, and will occasionally get you into trouble where "in and of itself" won't.

"In" gets used so many ways, in so many different combinations, that if you don't clarify its function by using the "in and of" construction, it can erroneously appear to be teamed up with the wrong word: "The fish the dog brought in itself wasn't the problem."

It's a slight archaism. I think, but "of itself" is different from "in itself", meaning "of its own volition". So "in and of itself" would mean something like "inherently and deliberately".

Something like.

Perhaps it means that it isn't evil, whether observed from within or without. I see an internal vs. external reference in "in and of".

It's an expensive book ($35 to $40 US), but _The American Heritage Dictionary of Idioms_ would be a very useful book for those learning English as a second language. Other less expensive books are available, too.

I've been supportive of what Teresa Nielsen Hayde writes, but her example this time wasn't that helpful to me. For the distinction to be made by example, I need to substitute "in and of" for "in" and then be able to see that one version is clearer than the other. I can't do that with her example. If I change it to "The fish the dog brought in and of itself wasn't the problem," I'm pretty much stuck with my original problem with understanding the sentence.

That problem is caused, at least partially, by having "in itself" or "in and of itself" so far removed from "fish." "In and of itself, the fish the dog brought in wasn't the problem." "In itself, the fish the dog brought in wasn't the problem." The sentence just doesn't work the other way. "The fish the dog brought in wasn't the problem" also works, but has a slightly different meaning.

Some difficulty may also stem from being able to say either "dog brought" or "dog brought in." I'd opt for "dog brought in"--not dissimilar to the saying, "Look what the cat dragged in." If I refer to the "fish the dog brought," it almost sounds to me as if the dog bought and then brought a gift to a party's hostess. If I refer to the "fish the dog brought in," there's more a sense of finding the fish and bringing it in, something much more likely for a dog to do.

What WAS the problem? It was either the smell or the fish guts falling on the floor. (Alternatively: It was either the smell or the fish's guts falling on the floor.)

The phrase "in and of itself" has become so cliched, I think it should be avoided. To me, "in itself" sounds much better.

Erle... all that stuff about fish and dogs only serves to confuse the issue. :-)
The question was, in my opinion, clearly answered by John Peacock below.
To that I'd also like to add that the prevalence of this phrase is likely due to the fact that those using it do so in the (mistaken) belief that it has more gravitas than simply saying "in itself".

"in and of itself" is an Americanism for "itself":
The fish itself wasn't the problem; The fish the dog brought in wasn't itself the problem; (and there are probably other constructions). The problem itself is that to British ears, "in and of" doesn't add any value whatsoever. We normally are content with "itself" itself, or when we really need a preposition, "in itself".

"The fish THAT the dog brought in wasn't, itself, the problem. Rather, it was the ensuing debate about pompous grammatical constructions that proved confounding."

I hate to beat a dead horse, but here're my two cents: "in and of" is superfluous. Itself as used here is an intensive pronoun, so further emphasis shouldn't be necessary.

Actually, I find it funny that I stumbled across this blog by Googling (is that a good term to use either??) the term "per say" or "per-say" and the Urban Dictionary website said it means "in-and-of-itself" and "in and of itself". Now I'm really confused on which one to use because I don't like either one of them, per say?? There's some word fun for you if anyone else stumbles in here.

Funny that "per say" led you to this, as it is also an incorrect (Americanized) spelling for this Latin expression, which actually means "by itself" and should be spelled "per se".
http://en.wiktionary.org/wiki/per_se

Ironically, English is not my first language, but I regularly find myself correcting English natives's writing. Now I know why I had to suffer learning Latin languages for endless hours...